Biodiesel-Oriented Microbial Lipid Research

Abstract

Biodiesel is a mixture of long-chain fatty acid methyl esters. It was made from vegetable oil and fats, and is renewable with outstanding combustion profile. It will be beneficial to meet ever-growing energy demanding if biodiesel is widely applied. On the other hand, carbohydrates, either from starchy material or lignocellulosic biomass, are the most abundant renewable resources. In this context, it is pivotal to convert carbohydrates into products with similar properties to conventional fossil fuel. Some microorganisms can accumulate lipid to more than 20 wt% of their biomass when carbohydrates or related carbon sources are metabolized. Microbial lipid, especially produced by yeasts, consists mainly of triacylglycerides with fatty acid compositional profile similar to those of the commercial vegetable oils. Because it can be obtained from renewable raw materials, and be produced continuously with no extensive arable land requirement, microbial lipid has been considered as potential feedstock for biodiesel industry and an important topic for industrial biotechnology. Microbial lipid production is an aerobic biochemical process that generates intracellular lipid using organic substrates. During the past few years, we have advocated the proposal of Biomass-to-Biodiesel that produces biodiesel using lignocellulosic materials. This proposal included three steps, 1) Hydrolysis of lignocellulose to carbohydrates; 2) Lipid production with oleaginous microorganisms; and 3) Transesterification of microbial lipid to biodiesel. We identified a hand of outstanding oleaginous yeasts, including Rhodosporidium toruloides, Lipomyces starkeyi, and Cryptococcus curvatus. These yeasts produced microbial lipid using materials including glucose, xylose, N-acetylglucosamine, raw glycerol, corn stalk hydrolysates and Jerusalem artichoke juice. We optimized lipid production processes. When using the yeast R. toruloides Y4 as the lipid producer in a 15-L bioreactor, we achieved lipid content, production titer and lipid productivity of over 65 wt%, 100 g/L and 0.8 g/l/h, respectively. We also demonstrated that biodiesel can be produced using either oleaginous microbial biomass or microbial lipid as the feedstock. Taken together, we will report the most recent progresses in biodiesel-oriented microbial lipid research in Dalian Institute of Chemical Physics, Chinese Academy of Sciences